U.S. patent number 7,444,803 [Application Number 11/290,642] was granted by the patent office on 2008-11-04 for exhaust gas control apparatus for engine and method for producing same.
This patent grant is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Yasunori Iwamoto, Masaharu Kuroda, Toshio Murata, Yasuhiro Nobata.
United States Patent |
7,444,803 |
Iwamoto , et al. |
November 4, 2008 |
Exhaust gas control apparatus for engine and method for producing
same
Abstract
An exhaust gas control apparatus for an engine and a method for
producing the same are provided. The exhaust gas control apparatus
includes a valve portion, an absorption portion, and a catalyst
portion. The valve portion includes a valve that opens/closes a
main exhaust passage. The absorption portion includes a
hydrocarbon-absorbent that absorbs hydrocarbons. The catalyst
portion includes a three-way catalyst that purifies exhaust gas.
The valve portion, absorption portion, and the catalyst portion are
independent of each other. The valve portion, the absorption
portion, and the catalyst portion are connected to each other in
series. With this configuration, any individual component can be
replaced with another corresponding component that achieves a
required level of performance while minimizing the number of other
components.
Inventors: |
Iwamoto; Yasunori (Toyota,
JP), Kuroda; Masaharu (Toyota, JP), Nobata;
Yasuhiro (Toyota, JP), Murata; Toshio (Toyota,
JP) |
Assignee: |
Toyota Jidosha Kabushiki Kaisha
(Toyota, JP)
|
Family
ID: |
36582209 |
Appl.
No.: |
11/290,642 |
Filed: |
December 1, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060123772 A1 |
Jun 15, 2006 |
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Foreign Application Priority Data
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Dec 15, 2004 [JP] |
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2004-363563 |
May 9, 2005 [JP] |
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2005-136147 |
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Current U.S.
Class: |
60/288; 60/274;
60/287; 60/292; 60/295; 60/297; 60/299 |
Current CPC
Class: |
F01N
3/0814 (20130101); F01N 3/0835 (20130101); F01N
3/0878 (20130101); F01N 13/0097 (20140603) |
Current International
Class: |
F01N
3/00 (20060101) |
Field of
Search: |
;60/274,285,287,288,292,295,296,300,324,299,297 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A 5-59942 |
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Mar 1993 |
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JP |
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A 2000-345829 |
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Dec 2000 |
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JP |
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A 2001-115830 |
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Apr 2001 |
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JP |
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Primary Examiner: Tran; Binh Q
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. An exhaust gas control apparatus for an engine, comprising: an
absorption portion that includes a first exhaust passage and a
second exhaust passage, the respective openings of which are
located at different positions, and through which exhaust gas flows
into the absorption portion; wherein the first exhaust passage is
provided therein with a hydrocarbon-absorbent, which absorbs
hydrocarbons present in the exhaust gas; a valve portion that
includes a valve that opens and closes the second exhaust passage,
thereby changing a mode where the exhaust gas flows; and a catalyst
portion that includes a catalyst that purifies the exhaust gas,
wherein the absorption portion, the valve portion, and the catalyst
portion are independent of each other; the absorption portion, the
valve portion, and the catalyst portion are connected to each other
in series, and the first exhaust passage communicates with a space
upstream of the second exhaust passage through an upstream-opening
positioned upstream of the hydrocarbon-absorbent, and communicates
with a space downstream of the second exhaust passage through a
downstream-opening positioned downstream of the
hydrocarbon-absorbent, when the valve is open, the exhaust gas
flows from the valve through the second exhaust passage to the
catalyst and a portion of the exhaust gas flows back from the
downstream-opening through the first exhaust passage and the
upstream-opening to the space upstream of the valve.
2. The exhaust gas control apparatus for an engine, according to
claim 1, wherein the valve portion, the absorption portion, and the
catalyst portion are disposed from an upstream side to a downstream
side.
3. The exhaust gas control apparatus for an engine according to
claim 1, wherein, when the valve is closed, the exhaust gas flows
from the space upstream of the valve through the upstream-opening,
the first exhaust passage and the downstream-opening to
catalyst.
4. The exhaust gas control apparatus for an engine according to
claim 1, wherein, when the valve is open, the downstream-opening
facilitates the flow of the exhaust gas between the first exhaust
passage and a space where pressure of the exhaust gas is
stable.
5. The exhaust gas control apparatus for an engine according to
claim 1, wherein the downstream-opening is positioned at a distance
from a boundary between a space where the exhaust gas swirls or
stagnates and a space where the exhaust gas does not swirl or
stagnate when the valve is open, and the distance is sufficient for
the exhaust gas to flow between the first exhaust passage and the
space where the exhaust gas does not swirl or stagnate when the
valve is open.
6. The exhaust gas control apparatus for an engine according to
claim 1, wherein an inlet port, through which the exhaust gas flows
into the exhaust gas control apparatus, is positioned such that a
straight flow of the exhaust gas from the inlet port does not pass
through the upstream-opening.
7. The exhaust gas control apparatus for an engine according to
claim 1, wherein the exhaust gas flows into the exhaust gas control
apparatus; and the upstream-opening is positioned such that a
straight flow of the exhaust gas from the inlet port does not pass
through the upstream-opening.
8. The exhaust gas control apparatus for an engine according to
claim 1, wherein an inlet port of an exhaust pipe that allows the
exhaust gas from the engine to flow therethrough is disposed
immediately upstream of the valve, and the exhaust gas flows into
the exhaust gas control apparatus through the inlet port.
9. The exhaust gas control apparatus for an engine according to
claim 1, wherein an auxiliary-exhaust pipe, which is independent of
an exhaust pipe that allows the exhaust gas from the engine to flow
therethrough, is connected to a downstream end of the exhaust pipe
and disposed immediately upstream of the valve so that a
downstream-opening of the auxiliary-exhaust pipe is disposed
immediately upstream of the valve to form an inlet port, through
which the exhaust gas flows into the exhaust gas control
apparatus.
10. The exhaust gas control apparatus for an engine according to
claim 9, wherein the auxiliary-exhaust pipe includes a hole which
radially communicates between an inside and an outside of the
auxiliary-exhaust pipe so as to allow the exhaust gas to flow
therethrough.
11. The exhaust gas control apparatus for an engine according to
claim 8, wherein a downstream-opening of the exhaust pipe is
disposed immediately upstream of the valve to function as the inlet
port.
12. The exhaust gas control apparatus for an engine according to
claim 11, wherein the exhaust pipe includes a hole, positioned
inside the valve portion, which radially communicates between an
inside and an outside of the exhaust pipe so as to allow the
exhaust gas to flow therethrough.
13. The exhaust gas control apparatus for an engine according to
claim 2, wherein the upstream-opening is positioned near the valve,
and the downstream-opening is positioned near the catalyst.
14. The exhaust gas control apparatus for an engine according to
claim 1, wherein, when the valve is open, the upstream-opening
facilitates the flow of the exhaust gas between the first exhaust
pipe and a space where the exhaust gas does not swirl or stagnate
and the downstream-opening facilitates the flow of exhaust gas
between the first exhaust passage and a space where the exhaust gas
swirls or stagnates.
15. The exhaust gas control apparatus for an engine according to
claim 1, wherein a restrictive element, which reduces a flow speed
of the exhaust gas flowing toward the downstream side through the
downstream-opening,is provided downstream of the
downstream-opening.
16. The exhaust gas control apparatus for an engine according to
claim 15, wherein the restrictive element is the catalyst.
17. The exhaust gas control apparatus for an engine according to
claim 15, wherein the restrictive element is a sound-absorbing
material.
18. The exhaust gas control apparatus for an engine according to
claim 1, wherein a relation between a cross sectional area of the
upstream-opening and a cross sectional area of the
downstream-opening is set so that a flow speed of the exhaust gas
flowing in the first exhaust passage is reduced to a speed that is
equal to or lower than an upper limit flow speed, at or below which
the hydrocarbon-absorbent can absorb all hydrocarbons present in
the exhaust gas, when the valve is closed.
19. An exhaust gas control apparatus for an engine, comprising: an
absorption portion that includes an external cylinder, disposed at
an outermost position thereof, a first exhaust passage and a second
exhaust passage, the respective openings of which are located at
different positions, and through which exhaust gas flows into the
abosorption portion; and the first exhaust passage is provided with
a hydrocarbon-absorbent which absorbs hydrocarbons present in the
exhaust gas, and a partition that is provided downstream of the
hydrocarbon-absorbent and that separates the first exhaust passage
from a first space, the first space being positioned on a
downstream side of the absorption portion and on a downstream side
of the second exhaust passage, the partition portion being provided
with at least one hole through which the exhaust gas flows between
the first exhaust passage and the first space; a valve portion that
includes an external cylinder, disposed at an outermost position
thereof, and a valve, connected to the external cylinder to face
the second exhaust passage, that opens and closes the second
exhaust passage, thereby changing a mode where the exhaust gas
flows; and a catalyst portion that includes an external cylinder,
disposed at an outermost position thereof, and a catalyst that
purifies the exhaust gas, wherein the absorption portion, the valve
portion, and the catalyst portion are independent of each other;
and the absorption portion, the valve portion, and the catalyst
portion are connected to each other with the external
cylinders.
20. The exhaust gas control apparatus for an engine according to
claim 19, wherein the catalyst is disposed so that all of the
exhaust gas flowing into a space inside the external cylinder of
the catalyst portion passes through the catalyst.
21. The exhaust gas control apparatus for an engine according to
claim 19, further comprising: a heat-insulating portion that
suppresses heat transmission from the second exhaust pipe to the
hydrocarbon-absorbent.
22. The exhaust gas control apparatus for an engine according to
claim 19, wherein the absorption further includes an internal
cylinder disposed inside the external cylinder; the first exhaust
passage is provided between the external cylinder and the internal
cylinder of the absorption portion; and the second exhaust passage
is provided inside the internal cylinder.
23. The exhaust gas control apparatus for an engine according to
claim 22, wherein the internal cylinder includes a plurality of
pipes that are concentrically disposed; and a space is formed
between the adjacent pipes.
24. The exhaust gas control apparatus for an engine according to
claim 23, wherein the heat-insulating material is disposed in the
space between any two adjacent pipes.
25. The exhaust gas control apparatus for an engine according to
claim 19, wherein the second exhaust passage has a tapered shape;
and a cross sectional area of the second exhaust passage orthogonal
to an axis thereof increases from an upstream side toward a
downstream side.
26. The exhaust gas control apparatus for an engine according to
claim 19, wherein the second exhaust passage allows the exhaust gas
to flow therethrough without passing through the
hydrocarbon-absorbent.
27. The exhaust gas control apparatus for an engine according to
claim 1, wherein the first structure includes an upstream-opening
positioned upstream of the hydrocarbon-absorbent, and a
downstream-opening positioned downstream of the
hydrocaron-absorbent; the upstream-opening allows the exhaust gas
to communicate between a space in which the hydrocarbon-absorbent
is provided and a space upstream of the upstream-opening and the
downstream-opening allows the exhaust gas to communicate between a
space in which the hydrocarbon-absorbent is provided and a space
downstream of the downstream-opening; and the downstream-opening is
positioned so as to stabilize a flow speed of the sidestream.
28. The exhaust gas control apparatus for an engine according to
claim 27, wherein, when the second mode is selected, pressure in a
space downstream of the downstream-opening is increased so as to be
higher than pressure in a space upstream of the
upstream-opening.
29. The exhaust gas control apparatus for an engine according to
claim 1, wherein the exhaust gas flows through an inlet port into
the exhaust gas control apparatus from an exhaust pipe located
upstream of the exhaust gas control apparatus; and the inlet port
is positioned so that a hydrocarbon concentration in the exhaust
gas in the mainstream is equal to or less than an upper limit
concentration, at or below which the catalyst can remove all
hydrocarbons present in the exhaust gas.
30. The exhaust gas control apparatus for an engine according to
claim 1, wherein the exhaust gas flows into the exhaust gas control
apparatus through an inlet port; a diameter of the inlet port is
set so that a hydrocarbon concentration in the exhaust gas of the
mainstream is equal to or less than an upper limit concentration,
at or below which the catalyst can remove all hydrocarbons present
in the exhaust gas.
31. An exhaust gas control apparatus for an engine, comprising; a
first structure that includes an external cylinder, disposed at an
outermost position thereof, a first exhaust passage and a second
exhaust passage, the respective openings of which are located at
different positions, and through which exhaust gas flows into the
first structure; and the first exhaust passage is provided with a
hydrocarbon-absorbent, which absorbs hydrocarbons present in
exhaust gas discharged from an engine, and a partition that is
provided downstream of the hydrocarbon-absorbent and that separates
the first exhaust passage from a first space, the first space (1)
being positioned on a downstream side of the first structure and on
a downstream side of the second exhaust passage and being radially
outside an extended cross-section of the second passage, the
partition portion being provided with at least one hole through
which the exhaust gas flows between the first exhaust passage and
the first space, the at least one hole being positioned radially
outside of the second passage; and a second structure disposed
downstream of the first structure, the second structure including
an external cylinder, disposed at an outermost position thereof,
and a catalyst, that purifies the exhaust gas discharged from the
engine, wherein the first structure and the second structure are
independent of each other; and the first structure and the second
structure are disposed in series, and are joined to each other, and
the first structure and the second structure are connected to each
other with the external cylinders.
32. A method for producing an exhaust gas control apparatus for an
engine, comprising; selecting an absorption portion that achieves a
required level of performance from among different absorption
portions that achieve different levels of performance, wherein each
of the absorption portions includes an external cylinder, disposed
at an outermost position thereof, a first exhaust passage and a
second exhaust passage, the respective openings of which are
located at different positions, and through which the exhaust gas
flows into the absorption portion; and the first exhaust passage is
provided with a hydrocarbon-absorbent that absorbs hydrocarbon
present in the exhaust gas, and a partition that is provided
downstream of the hydrocarbon-absorbent and that separates the
first exhaust passage from a first space, the first space being
positioned on a downstream side of the absorption portion and on a
downstream side of the second exhaust passage, the partition
portion being provided with at least one hole through which the
exhaust gas flows between the first exhaust passage and the first
space; selecting a valve portion that achieves a required level of
performance from among different valve portions that achieve
different levels of performance, wherein each of the valve portions
includes an external cylinder, disposed at an outermost position
thereof, and a valve, connected to the external cylinder to face
the second exhaust passage, that opens and closes the second
exhaust passage; and each of the valve portions changes a mode
where the exhaust gas flows by opening and closing the second
exhaust passage, using the valve; selecting a catalyst portion that
achieves a required level of performance from among different
catalyst portions that achieve different levels of performance,
wherein each of the catalyst includes an external cylinder,
disposed at an outermost position thereof, and a catalyst that
purifies the exhaust gas; and disposing, in series, the absorption
portion selected in the first step, the valve portion selected in
the second step and the catalyst portion selected in the third
step, and that are independent of each other, and the absorption
portion, the valve portion, and the catalyst portion are connected
to each other with the external cylinders.
33. The method for producing the exhaust gas control apparatus for
an engine according to claim 32, wherein an auxiliary-exhaust pipe,
which is independent of an exhaust pipe positioned upstream of the
exhaust gas control apparatus, is connected to an end at a
downstream side of the exhaust pipe; the auxiliary-exhaust pipe
includes an opening positioned at a downstream side thereof; and
the opening of the auxiliary-exhaust pipe is disposed immediately
upstream of the valve.
34. The method for producing the exhaust gas control apparatus for
an engine according to claim 33, wherein a hole, which allows the
exhaust gas to radially flow between an inside and an outside of
the auxiliary-exhaust pipe, is formed in the auxiliary-exhaust pipe
before the auxiliary-exhaust pipe is connected to the exhaust
pipe.
35. The method for producing the exhaust gas control apparatus for
an engine according to claim 34, wherein the exhaust pipe includes
an opening positioned at a downstream side thereof, and the opening
of the exhaust pipe is disposed immediately upstream of the
valve.
36. The method for producing the exhaust gas control apparatus for
an engine according to claim 35, wherein a hole, which allows the
exhaust gas to radially flow between an inside and an outside of
the exhaust pipe, is formed in a portion of the exhaust pipe
located inside the valve portion, before the exhaust pipe is
disposed immediately upstream the valve portion.
Description
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2004-363563 filed
on Dec. 15, 2004 and No. 2005-136147 filed on May 9, 2005,
including the specification, drawings and abstract is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
The invention relates to an exhaust gas control apparatus for an
engine, which includes a hydrocarbon-absorbent that absorbs
hydrocarbons present in exhaust gas.
DESCRIPTION OF THE RELATED ART
Exhaust gas control apparatuses for an engine remove nitrogen
oxide, carbon monoxide, and hydrocarbons using a three-way
catalyst. However, when the temperature of the three-way catalyst
is low, the exhaust gas control apparatuses unable to remove
hydrocarbons efficiently.
Japanese Patent Application Publication No. JP-A-2000-345829
(hereinafter, referred to as "No. 2000-345829") discloses an
exhaust gas control apparatus including a hydrocarbon-absorbent
that temporarily captures hydrocarbons.
In the exhaust gas control apparatus including a
hydrocarbon-absorbent disclosed in No. 2000-345829, the
hydrocarbon-absorbent absorbs hydrocarbons when the temperature of
a three-way catalyst is low, and releases the hydrocarbons to the
three-way catalyst when the three-way catalyst can remove
hydrocarbons. With this configuration, hydrocarbons present in
exhaust gas can be appropriately removed.
In the exhaust gas control apparatus described in No. 2000-345829,
when the three-way catalyst is replaced with another one having a
larger cross sectional area, which improves the performance of
exhaust gas purification and reduces back pressure, the associated
components in the exhaust gas control apparatus (i.e., a casing, a
pipe, and the hydrocarbon-absorbent) also need to be replaced with
corresponding components in accordance with the size of the
three-way catalyst.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide
an exhaust gas control apparatus for an engine, where the
components can be individually replaced with another one based on
the required level of performance while minimizing the number of
other components to be replaced, and a method for producing the
same.
According to an aspect of the invention, an exhaust gas control
apparatus for an engine includes an absorption portion, a valve
portion, and a catalyst portion. The absorption portion includes a
first exhaust passage and a second exhaust passage, and a
hydrocarbon-absorbent. The first exhaust passage and the second
exhaust passage have respective openings located at different
positions. The openings allow exhaust gas discharged from an engine
to flow into the absorption portion. The hydrocarbon-absorbent is
provided within the first exhaust passage, and absorbs hydrocarbons
present in the exhaust gas. The valve portion includes a valve that
opens/closes the second exhaust passage. The valve portion changes
the mode where the exhaust gas flows by opening/closing the second
exhaust passage using the valve. The catalyst portion includes a
catalyst that purifies the exhaust gas. The absorption portion, the
valve portion, and the catalyst portion are independent of each
other. The absorption portion, the valve portion, and the catalyst
portion are connected to each other in series.
In the exhaust gas control apparatus having the above
configuration, each of the absorption portion, the valve portion,
and the catalyst portion can each be replaced independently of the
other portions with another corresponding portion to achieve the
required level of performance. Therefore, for example, the size of
the catalyst can be changed without replacing the
hydrocarbon-absorbent. With this configuration, any individual
component may be replaced with another corresponding component to
achieve the required level of performance while minimizing the
number of other components to be replaced.
According to another aspect of the invention, an exhaust gas
control apparatus includes a first structure, a second structure,
and a third structure. The first structure includes a
hydrocarbon-absorbent that absorbs hydrocarbons present in exhaust
gas discharged from an engine. The second structure includes a
catalyst that purifies the exhaust gas discharged from the engine.
The third structure changes the mode where the exhaust gas flows
between two modes. In one mode, all of the exhaust gas passes
through the hydrocarbon-absorbent. In another mode, part of the
exhaust gas does not pass through the hydrocarbon-absorbent. The
first structure, the second structure, and the third structure are
independent of each other. The first structure, the second
structure, and the third structure are disposed in series, and are
joined to each other.
In the exhaust gas control apparatus for an engine having the
aforementioned configuration, each of the first structure, the
second structure, and the third structure can be replaced
independently of the other portions with another corresponding
structure to achieve the required level of performance. Therefore,
for example, the size of the catalyst can be changed without
replacing the hydrocarbon- absorbent. With this configuration, any
individual structure may be replaced with another corresponding
structure to achieve the required level of performance while
minimizing the number of other components to be replaced.
According to another aspect of the invention, an exhaust gas
control apparatus includes a first structure, and a second
structure. The first structure includes a hydrocarbon-absorbent
that absorbs hydrocarbons present in exhaust gas discharged from an
engine. The second structure includes a catalyst that purifies the
exhaust gas discharged from the engine. The first structure and the
second structure are independent of each other. The first structure
and the second structure are disposed in series, and are joined to
each other.
In the exhaust gas control apparatus for an engine having the
aforementioned configuration, each of the first structure and the
second structure may be replaced independently of the other
structure with another corresponding structure to achieve the
required level of performance. Therefore, for example, the size of
the catalyst can be changed without replacing the
hydrocarbon-absorbent. With this configuration, any individual
component may be replaced with another corresponding component to
achieve the required level of performance while minimizing the
number of other components to be replaced.
According to another aspect of the invention, a method for
producing an exhaust gas control apparatus for an engine, which
includes a catalyst that purifies exhaust gas discharged from an
engine, and a hydrocarbon-absorbent that absorbs hydrocarbons
present in the exhaust gas. The method includes a first step of
selecting an absorption portion that achieves the required level of
performance; a second step of selecting a valve portion that
achieves the required level of performance; a third step of
selecting a catalyst portion that achieves the required level of
performance; and a fourth step of disposing the selected absorption
portion, the valve portion, and the catalyst portion in series, and
joining them to each other. Each valve portion includes a first
exhaust passage and a second exhaust passage, and a
hydrocarbon-absorbent. The first exhaust passage and the second
exhaust passage include respective openings located at different
positions, and the openings allow the exhaust gas to flow into the
absorption portion. The hydrocarbon-absorbent is provided in the
first exhaust passage, and absorbs hydrocarbons present in the
exhaust gas. Each valve portion includes a valve that opens/closes
the second exhaust passage. Each valve portion changes the mode
where the exhaust gas flows by opening/closing the second exhaust
passage using the valve. Each catalyst portion includes the
catalyst.
In the exhaust gas control apparatus having the aforementioned
configuration and the method for producing the same, the exhaust
gas control apparatus is formed by selecting the absorption
portion, the valve portion, and the catalyst portion that achieve
the respective required levels of performance, and joining them to
each other. Therefore, when producing different types of exhaust
gas control apparatuses, any individual component may be replaced
with another corresponding component that achieves the required
level of performance while minimizing the number of other
components to be replaced.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, advantages thereof, and technical industrial
significance of this invention will be better understood by reading
the following detailed description of the example embodiments of
the invention, when considered in connection with the accompanying
drawings, in which:
FIG. 1 illustrates the entire configuration of an exhaust system to
which an exhaust gas control apparatus for an engine according to
an embodiment of the invention is applied;
FIG. 2 illustrates the plane view of a catalytic-converter with an
absorbent in the exhaust gas control apparatus for an engine
according to the embodiment;
FIG. 3 illustrates the plane view of a valve portion in the exhaust
gas control apparatus for an engine according to the
embodiment;
FIG. 4 illustrates the front view from the perspective indicated by
an arrow V1 in FIG. 3, of the valve portion in the exhaust gas
control apparatus for an engine according to the embodiment;
FIG. 5 illustrates the front view from the perspective indicated by
an arrow V2 in FIG. 3, of the valve portion in the exhaust gas
control apparatus for an engine according to the embodiment;
FIG. 6 illustrates the cross sectional view taken along line D4-D4
in FIG. 4, of the valve portion in the exhaust gas control
apparatus for an engine according to the embodiment;
FIG. 7 illustrates the plane view of an absorption portion in the
exhaust gas control apparatus for an engine according to the
embodiment;
FIG. 8 illustrates the front view from the perspective indicated by
an arrow V3 in FIG. 7, of the absorption portion in the exhaust gas
control apparatus for an engine according to the embodiment;
FIG. 9 illustrates the front view from the perspective indicated by
an arrow V4 in FIG. 7, of the absorption portion in the exhaust gas
control apparatus for an engine according to the embodiment;
FIG. 10 illustrates the cross sectional view taken along line D8-D8
in FIG. 8, of the absorption portion in the exhaust gas control
apparatus for an engine according to the embodiment;
FIG. 11 illustrates the plane view of a catalyst portion in the
exhaust gas control apparatus for an engine according to the
embodiment;
FIG. 12 illustrates the front view from the perspective indicated
by an arrow V5 in FIG. 11, of the catalyst portion in the exhaust
gas control apparatus for an engine according to the
embodiment;
FIG. 13 illustrates the front structure from the perspective
indicated by an arrow V6 in FIG. 11, of the catalyst portion in the
exhaust gas control apparatus for an engine according to the
embodiment;
FIG. 14 illustrates the cross sectional view taken along line
D12-D12 in FIG. 12, of the exhaust gas control apparatus according
to the embodiment;
FIG. 15 illustrates the cross sectional view taken along line D2-D2
in FIG. 2, of a catalytic-converter with an absorbent in the
exhaust gas control apparatus for an engine according to the
embodiment;
FIG. 16 illustrates the cross sectional view taken along line D2-D2
in FIG. 2, of the catalytic-converter with the absorbent in the
exhaust gas control apparatus for an engine according to the
embodiment;
FIG. 17 illustrates the enlarged view of the structure near a
partition in the exhaust gas control apparatus for an engine
according to the embodiment;
FIG. 18 illustrates the enlarged view of the structure near the
partition in the exhaust gas control apparatus for an engine
according to the embodiment;
FIG. 19 illustrates the flow of exhaust gas in the exhaust gas
control apparatus for an engine according to the embodiment where
the valve is closed;
FIG. 20 illustrates the flow of exhaust gas in the exhaust gas
control apparatus for an engine according to the embodiment where
the valve is open;
FIG. 21 illustrates the cross sectional view of a
catalytic-converter with an absorbent in an exhaust gas control
apparatus for an engine according to another embodiment, taken
along the axis thereof;
FIG. 22 illustrates the cross sectional view of a
catalytic-converter with an absorbent in an exhaust gas control
apparatus for an engine according to another embodiment, taken
along the axis thereof;
FIG. 23 illustrates the cross sectional view of a
catalytic-converter with an absorbent in an exhaust gas control
apparatus for an engine according to another embodiment, taken
along the axis thereof; and
FIG. 24 illustrates the cross sectional view of a
catalytic-converter with an absorbent in an exhaust gas control
apparatus for an engine according to another embodiment, taken
along the axis thereof.
DETAILED DESCRIPTION OF THE EXEMPLE EMBODIMENTS
In the following description and the accompanying drawings, the
present invention will be described in more detail with reference
to example embodiments. An example embodiment of the invention will
be described with reference to FIG. 1 through FIG. 20. In this
embodiment, the phrase "exhaust gas flows from the upstream side to
the downstream side" signifies that exhaust gas flows from the
engine toward the atmosphere.
FIG. 1 illustrates the structure of an engine exhaust system. The
exhaust system for an engine 1 includes a catalytic-converter 21, a
catalytic-converter 3 with an absorbent, and a muffler 22.
The engine 1 is connected to the catalytic-converter 21 via a first
exhaust pipe 23. The catalytic-converter 21 is connected to the
catalytic-converter 3 via a second exhaust pipe 24.
The catalytic-converter 3 is connected to the muffler 22 via a
third exhaust pipe 25. FIG. 2 illustrates the entire structure of
the catalytic-converter 3.
The catalytic-converter 3 includes a valve portion 4 (third
structure), an absorption portion 5 (first structure), and a
catalyst portion 6 (second structure). The valve portion changes
the mode where the exhaust gas flows in the catalytic-converter 3.
The absorption portion 5 includes an absorbent that absorbs
hydrocarbon in exhaust gas. The catalyst portion 6 includes a
catalyst that purifies exhaust gas.
In the catalytic-converter 3, the valve portion 4, the absorption
portion 5, and the catalyst portion 6 are arranged in the stated
order from the upstream side to the downstream side. These portions
are independent of each other.
In the catalytic-converter 3, the valve portion 4 is connected to
the upstream-side of the absorption portion 5, and the catalyst
portion 6 is connected to the downstream-side of the absorption
portion 5. The second exhaust pipe 24 is connected to the
upstream-side of the valve portion 4. The third exhaust pipe 25 is
connected to the downstream-side of the catalyst portion 6.
Hereinafter, the structure of each portion will be described.
[1] The structure of the valve portion will be described. FIG. 3
illustrates the plane view of the valve portion 4. FIG. 4
illustrates the front view of the valve portion 4 from the
perspective indicated by an arrow V1 in FIG. 3.
FIG. 5 illustrates the front view of the valve portion 4 from the
perspective indicated by an arrow V2 in FIG. 3. FIG. 6 illustrates
the cross sectional view of the valve portion 4 taken along line
D4-D4 in FIG. 3. The valve portion 4 includes an external cylinder
41 that is the main body of the valve portion 4.
The external cylinder 41 encloses the valve portion 4. The external
cylinder 41 includes an opening 42 positioned at the upstream side
thereof, and an opening 43 positioned at the downstream side
thereof.
The opening 42 allows exhaust gas to flow between the space
upstream of the valve portion 4 and the space inside the valve
portion 4. The second exhaust pipe 24 is inserted in the opening
42. That is, the inner diameter of the opening 42 is substantially
equal to the outer diameter of the second exhaust pipe 24.
Exhaust gas flows between the space inside the valve portion 4 and
the space downstream of the valve portion 4 through opening 43. The
absorption portion 5 is inserted in the opening 43 (i.e., the
external cylinder 51 of the absorption portion 5 is inserted in the
opening 43). That is, the inner diameter of the opening 43 is
substantially equal to the outer diameter of external cylinder 51
of the absorption portion 5.
A valve 44 changes the mode where the exhaust gas flows in the
catalytic-converter 3 and is provided inside the external cylinder
41 of the valve portion 4. The valve 44 is controlled to be
opened/closed by an electronic control unit that controls the
engine 1.
Next, the structure of the absorption portion will be described.
FIG. 7 illustrates the plane view of the absorption portion 5. FIG.
8 illustrates the front view of the absorption portion 5 from the
perspective indicated by an arrow V3 in FIG. 7.
FIG. 9 illustrates the front view of the absorption portion 5 from
the perspective indicated by an arrow V4 in FIG. 7. FIG. 10
illustrates the cross sectional view of the absorption portion 5
taken along line D8-D8 in FIG. 8. The absorption portion 5 includes
an external cylinder 51 that is the main body of the absorption
portion 5.
The external cylinder 51 encloses the absorption portion 5. The
external cylinder 51 includes an opening 52 positioned at the
upstream side thereof and an opening 53 positioned at the
downstream side thereof.
Exhaust gas flows between the space upstream of the absorption
portion 5 and the space inside the absorption portion 5 through
opening 52. The opening 52 is inserted in the valve portion 4.
Exhaust gas flows between the space inside the absorption portion 5
and the space downstream of the absorption portion 5 through
opening 53. The opening 53 is inserted in the catalyst portion 6
(i.e., the opening 53 is inserted in an external cylinder 61 of the
catalyst portion 6). That is, the outer diameter of the opening 53
is substantially equal to the inner diameter of the external
cylinder 61 of the catalyst portion 6.
An internal cylinder 54 of the absorption portion 5 is provided
within the external cylinder 51 of the absorption portion 5. A main
exhaust passage RA, which extends along the axis of the absorption
portion 5, is formed inside the internal cylinder 54. The main
exhaust passage RA corresponds to the second exhaust passage
according to the invention.
The internal cylinder 54 of the absorption portion 5 includes an
opening RA1 positioned at the upstream side thereof and an opening
RA2 positioned at the downstream side thereof. The opening RA1
allows exhaust gas to flow between the space upstream of the
internal cylinder 54 and the main exhaust passage RA.
Exhaust gas flows between the main exhaust passage RA and the space
downstream of the internal cylinder 54 through opening RA2. The
internal cylinder 54 is fixed to the external cylinder 51 such that
an end portion of the internal cylinder 54 at the upstream side
thereof protrudes from the external cylinder 51.
An outer exhaust passage RB is formed between the inner surface of
the external cylinder 51 and the outer surface of the internal
cylinder 54. The outer exhaust passage RB extends along the axis of
the absorption portion 5.
The opening 52 functions as the opening of the outer exhaust
passage RB at the upstream side thereof. Therefore, the opening 52
may also be referred to as "opening RB1". The opening 52 allows
exhaust gas to flow between the space upstream of external cylinder
51 and the outer exhaust passage RB.
The outer exhaust passage RB is provided with a
hydrocarbon-absorbent 55 that temporarily captures hydrocarbon
present in exhaust gas. A partition 57 is provided downstream of
the hydrocarbon-absorbent 55. The partition 57 separates the outer
exhaust passage RB from the space that is positioned downstream of
the main exhaust passage RA and the outer exhaust passage RB inside
the absorption portion 5 (i.e., a space 56 at the downstream side
of the absorption portion 5).
One end of the partition 57 is joined to the inner surface of the
external cylinder 51. The other end of the partition 57 is joined
to the outer surface of the internal cylinder 54. The partition 57
is provided with a plurality of holes (partition holes 57H) through
which exhaust gas flows between the outer exhaust passage RB and
the space 56 inside the absorption portion 5. That is, the
partition holes 57H function as the downstream-openings of the
outer exhaust passage RB. Therefore, the partition holes 57H may
also be referred to as "openings RB2". The openings RB2 correspond
to the downstream-opening according to the invention.
[3] Next, the structure of the catalyst portion will be described.
FIG. 11 illustrates the front view of the catalyst portion 6. FIG.
12 illustrates the front view of the catalyst portion 6 from the
perspective indicated by an arrow V5 in FIG. 11.
FIG. 13 illustrates the front view of the catalyst portion 6 from
the perspective indicated by an arrow V6 in FIG. 11. FIG. 14
illustrates the cross sectional view of the catalyst portion 6
taken along line D12-D12 in FIG. 12. The catalyst portion 6
includes an external cylinder 61 that is the main body of the
catalyst portion 6.
The external cylinder 61 encloses the catalyst portion 6. The
external cylinder 61 includes an opening 62 positioned at the
upstream side thereof and an opening 63 at the downstream side
thereof.
The opening 62 allows exhaust gas to flow between the space
upstream of the catalyst portion 6 and the space inside the
catalyst portion 6. The external cylinder 51 of the absorption
portion 5 is inserted in the opening 62. Exhaust gas flows between
the space inside the catalyst portion 6 and the space downstream of
the catalyst portion 6 through opening 63. The third exhaust pipe
25 is inserted in the opening 63. The inner diameter of the opening
63 is substantially equal to the outer diameter of the third
exhaust pipe 25.
A three-way catalyst 64 is provided inside the external cylinder 61
of the catalyst portion 6. The three-way catalyst 64 is disposed so
that all of the exhaust gas flowing into the catalyst portion 6
passes through the three-way catalyst 64. The structure inside the
catalyst converter 3 with the absorbent will be described with
reference to FIG. 15 and FIG. 16.
FIG. 15 illustrates the cross sectional view taken along line D2-D2
in FIG. 2, of the catalyst converter 3 with the absorbent when the
valve 44 is closed. FIG. 16 illustrates the cross sectional
structure taken along line D2-D2 in FIG. 2, of the
catalytic-converter 3 when the valve 44 is open.
In the catalytic-converter 3, the external cylinder 41 of the valve
portion 4 is joined to the external cylinder 51 of the absorption
portion 5, and the external cylinder 51 of the absorption portion 5
is joined to the external cylinder 61 of the catalyst portion 6.
The second exhaust pipe 24 inserted in the opening 42 is joined to
the external cylinder 41 of the valve portion 4.
The third exhaust pipe 25 inserted in the opening 63 is joined to
the external cylinder 61 of the catalyst portion 6. The portion of
the internal cylinder 54, which protrudes from the external
cylinder 51, is positioned in the space inside the valve portion 4.
The valve 44 is inserted in the opening RA1. Thus, the main exhaust
passage RA can be opened/closed using the valve 44.
The space 45 inside the valve portion 4 includes a space 45A
upstream of the opening RA1, and a space between the inner surface
of the external cylinder 41 and the outer surface of the internal
cylinder 54 (i.e., auxiliary-exhaust passage RC). The space 45A
corresponds to the space upstream of the valve according to the
invention.
The auxiliary-exhaust passage RC extends along the axis of the
valve portion 4. The opening RB1 allows exhaust gas to flow between
the auxiliary-exhaust passage RC and the outer exhaust passage
RB.
Exhaust gas flows between the auxiliary-exhaust passage RC and the
space 45A inside the valve portion 4 through an opening RC1
positioned at the upstream side of the auxiliary-exhaust passage
RC. The opening RC1 corresponds to the upstream-opening according
to the invention.
In the catalytic-converter 3, the auxiliary-exhaust passage RC and
the outer exhaust passage RB constitute a sub-exhaust passage RD.
The opening RC1 allows exhaust gas to flow between the space 45A
inside the valve portion 4 and the sub-exhaust passage RD. That is,
the opening RC1 functions as the upstream-opening of the
sub-exhaust passage RD. Also, the openings RB2 allow exhaust gas to
flow between the sub-exhaust passage RD and the space 56 inside the
absorption portion 5. That is, the openings RB2 function as the
openings of the sub-exhaust passage RD at the downstream side
thereof.
The sub-exhaust passage RD is parallel with the main exhaust
passage RA. Exhaust gas flowing through the main exhaust passage RA
does not pass through the hydrocarbon-absorbent 55. The
catalytic-converter 3 includes the valve portion 4, the absorption
portion 5, and the catalyst portion 6. With this configuration, the
mode where the exhaust gas flows can be changed as required.
Hereinafter, the modes where the exhaust gas flows, and the
configuration for allowing exhaust gas to flow in each mode will be
described.
[1] First, the direction of flow of exhaust gas in the sub-exhaust
passage (when the valve is open) will be described. When
hydrocarbons released from the hydrocarbon-absorbent 55 are not
sufficiently mixed with exhaust gas passing through the three-way
catalyst 64, the concentration of hydrocarbons may become
excessively high in the three-way catalyst 64. As a result, the
three-way catalyst 64 cannot sufficiently remove hydrocarbons, and
exhaust gas containing hydrocarbons is discharged to the
atmosphere.
In the catalytic-converter 3 according to this embodiment, when the
valve 44 is open, there is a reverse flow of exhaust gas in the
sub-exhaust passage RD from the downstream side to the upstream
side that flows into the space upstream of the valve 44. As such,
hydrocarbons released from the hydrocarbon-absorbent 55 are
sufficiently mixed with exhaust gas flowing through the main
exhaust passage RA before the hydrocarbons reach the three-way
catalyst 64. This improves the efficiency of the three-way catalyst
64 in removing hydrocarbons.
To allow exhaust gas to flow in the aforementioned mode, the
catalytic-converter 3 has the configuration described in the
following sections (a) through (e).
(a) The opening RC1 and the openings RB2 are positioned so that the
pressure upstream of the opening RC1 is lower than the pressure
downstream of the openings RB2 when the valve 44 is open. More
specifically, the opening RC1 and the openings RB2 are positioned
in the manner described in the following (b) and (c).
(b) The opening RC1 is positioned so as to allow exhaust gas to
flow between the sub-exhaust passage RD and a space upstream of the
sub-exhaust passage RD, where the exhaust gas does not swirl or
stagnate when the valve 44 is open. The openings RB2 are positioned
so as to allow exhaust gas to flow between the sub-exhaust passage
RD and a space downstream of the sub-exhaust passage RD, where the
exhaust gas swirls or stagnates when the valve 44 is open.
The pressure in the area where exhaust gas either swirls or
stagnates is higher than the pressure in the area where exhaust gas
does not swirl or stagnate. Therefore, in the aforementioned
configuration, exhaust gas stably flows in the sub-exhaust passage
RD from the downstream side to the upstream side when the valve 44
is open.
(c) The opening RC1 is positioned near the valve 44. The openings
RB2 are positioned near the three-way catalyst 64.
In the catalyst converter 3 with the absorbent, the three-way
catalyst 64 restricts the flow of exhaust gas, which makes the
pressure upstream of the three-way catalyst 64 higher than the
pressure near the valve 44. That is, by reducing the flow speed of
the exhaust gas the three-way catalyst 64 increases backpressure in
the exhaust system. Therefore, with this configuration, exhaust gas
stably flows in the sub-exhaust passage RD from the downstream side
to the upstream side when the valve 44 is open.
(d) An inlet port RE, through which exhaust gas in the second
exhaust pipe 24 flows into the catalytic-converter 3, is disposed
immediately upstream of the valve 44. In this embodiment, the
downstream-opening of the second exhaust pipe 24 functions as the
inlet port RE, and this opening is disposed immediately upstream of
the valve 44.
As the distance between the inlet port RE and the valve 44
decreases, the flow amount of exhaust gas flowing into the main
exhaust passage RA through the inlet port RE increases when the
valve 44 is open. That is, as the distance between the inlet port
RE and the valve 44 decreases, less exhaust gas flows into the
sub-exhaust passage RD through the inlet port RE. Thus, with this
configuration, the flow of the exhaust gas from the upstream side
to the downstream side is unlikely to interfere with the flow of
the exhaust gas from the downstream side to the upstream side in
the sub-exhaust passage RD. Therefore, exhaust gas stably flows in
the sub-exhaust passage RD from the downstream side to the upstream
side.
(e) As shown in FIG. 17, the inlet port RE is positioned so that a
straight flow of the exhaust gas from the inlet port RE (i.e., the
flow indicated by a straight line LA) does not pass through the
opening RC1. In this embodiment, the diameter of the inlet port RE
is less than the outer diameter of the internal cylinder 54 of the
absorption portion 5. Also, the axis of the second exhaust pipe 24
is substantially the same as the axis of internal cylinder 54 of
the absorption portion 5.
However, if the opening RC1 is disposed such that the straight flow
of the exhaust gas from the inlet port RE passes through the
opening RC1 and enters the sub-exhaust passage RD, the straight
flow of the exhaust gas would collide with the reverse flow of the
exhaust gas in the sub-exhaust passage RD. This would interfere
with the flow of the exhaust gas from the downstream side to the
upstream side in the sub-exhaust passage RD.
In the configuration in this embodiment, the inlet port RE is
positioned so as to avoid the aforementioned situation. Therefore,
exhaust gas stably flows in the sub-exhaust passage RD from the
downstream side to the upstream side.
[2] Next, the variation in the flow speed of the exhaust gas
flowing in the sub-exhaust passage (when the valve is open) will be
described. When the valve 44 is open, the flow speed of the exhaust
gas flowing in the sub-exhaust passage RD varies mainly depending
on the pressure downstream of the opening RB2. Meanwhile, the
amount of hydrocarbons released from the hydrocarbon-absorbent 55
varies depending on the flow speed of the exhaust gas. Therefore,
when the flow speed of the exhaust gas flowing in the sub-exhaust
passage RD varies greatly, the hydrocarbon content of the exhaust
gas flowing in the main exhaust passage RA will also vary greatly.
As a result, the exhaust gas containing an excessively high
concentration of hydrocarbons may flow into the three-way catalyst
64. This reduces the efficiency of the three-way catalyst 64 in
removing hydrocarbons.
Accordingly, the catalytic-converter 3 in this embodiment is
configured so that the flow speed of the exhaust gas flowing in the
sub-exhaust passage RD does not greatly vary. With this
configuration, the hydrocarbon content of the exhaust gas flowing
in the main exhaust passage RA does not greatly vary. This improves
the efficiency in removing hydrocarbons.
To allow the exhaust gas to flow in the aforementioned mode, the
catalytic-converter 3 is configured as described in the following
sections (a) and (b). (a) The openings RB2 are positioned so as to
allow exhaust gas to flow between the sub-exhaust passage RD and a
space where the pressure does not vary greatly (i.e., the pressure
is stable) in the absorption portion 5 when the valve 44 is open.
More specifically, the openings RB2 are positioned in the manner
described in the following (b).
(b) In FIG. 18, a boundary line LB indicates the boundary between a
space (i.e., space 56A) where exhaust gas swirls or stagnates and a
space where the exhaust gas does not swirl or stagnate. The
openings RB2 are positioned distant from the boundary line LB so as
to allow exhaust gas to flow between the sub-exhaust passage RD and
the space where exhaust gas swirls or stagnates (i.e., the space
56A). That is, the openings RB2 are positioned so as to allow
exhaust gas to flow between the sub-exhaust passage RD and the
space 56A positioned outside of the boundary line LB (i.e., the
space 56A near the external cylinder 51).
The pressure in the space furthest from the boundary line LB is
more stable than the pressure in the space near the boundary line
LB. Also, the pressure in the space where exhaust gas swirls or
stagnates is more stable than that in the space where the exhaust
gas does not swirl or stagnate. Therefore, with the aforementioned
configuration, the flow speed of the exhaust gas flowing in the
sub-exhaust passage RD does not greatly vary.
[3] Next, the flow speed of the exhaust gas flowing in the
sub-exhaust passage (when the valve is open) will be described. If
the concentration of hydrocarbons in the exhaust gas exceeds an
upper limit value at or below which the three-way catalyst 64 can
remove all of hydrocarbons present in the exhaust gas when the
valve 44 is open, some hydrocarbons will not be removed by the
three-way catalyst 64.
Accordingly, the catalytic-converter 3 in this embodiment is
configured to reduce the hydrocarbon concentration of the exhaust
gas flowing in the main passage RA to a level equal to or less than
the upper limit value. That is, the catalytic-converter 3 in this
embodiment is configured such that the hydrocarbon concentration in
the exhaust gas flowing in the main exhaust passage RA does not
exceed the upper limit value. With this configuration, the
three-way catalyst 64 can efficiently remove hydrocarbons.
To allow exhaust gas to flow in the aforementioned mode, the
catalytic-converter 3 is configured as described in the following
section (a). (a) The hydrocarbon concentration in the exhaust gas
flowing in the main exhaust passage RA greatly varies depending on
the amount of hydrocarbons released from the hydrocarbon-absorbent
55. That is, the hydrocarbon concentration of the exhaust gas
flowing in the main exhaust passage RA greatly varies depending on
the flow speed of the exhaust gas flowing in the sub-exhaust
passage RD. Meanwhile, the flow speed of the exhaust gas flowing in
the sub-exhaust passage RD varies depending on the position and the
diameter of the inlet port RE.
Accordingly, in this embodiment, the inlet port RE is appropriately
positioned and the diameter of the inlet port RE is appropriately
set so that the hydrocarbon concentration in the exhaust gas
flowing in the main exhaust passage RA is equal to or less than the
upper limit value.
The inlet port RE is appropriately positioned by adjusting the
distance between the inlet port RE and the valve 44 based on the
relation between the distance and the flow speed of the exhaust gas
flowing in the sub-exhaust passage RD. Also, the diameter of the
inlet port RE is appropriately adjusted by reducing the end portion
of the second exhaust pipe 24 in the radial direction based on the
relation between the diameter and the flow speed of the exhaust gas
flowing in the sub-exhaust passage RD. In some configurations of
the catalytic-converter 3, the diameter of the inlet port RE is
appropriately set by increasing the end portion of the second
exhaust pipe 24 in the radial direction.
[4] Next, the flow speed of the exhaust gas flowing in the
sub-exhaust passage when the valve is closed will be described. In
the case where the flow speed of the exhaust gas passing through
the hydrocarbon-absorbent 55 is excessively high when the valve 44
is closed, the exhaust gas passes through the hydrocarbon-absorbent
55 before the hydrocarbon-absorbent 55 absorbs hydrocarbons. That
is, in the case where the flow speed of the exhaust gas is higher
than an upper limit speed at or below which the
hydrocarbon-absorbent 55 can absorb hydrocarbons, the
hydrocarbon-absorbent 55 cannot absorb some hydrocarbons.
Accordingly, the catalytic-converter 3 in this embodiment is
configured so that the flow speed of the exhaust gas flowing in the
sub-exhaust passage RD does not exceed the upper limit speed when
the valve 44 is closed. In this configuration, the
hydrocarbon-absorbent 55 can absorb hydrocarbons present in exhaust
gas passing through the hydrocarbon-absorbent 55.
To allow exhaust gas to flow in the aforementioned mode, the
catalytic- converter 3 is configured as described in the following
sections (a) through (d). (a) The relation between the cross
sectional area of the opening RC1 and the total of cross sectional
areas of the openings RB2 is set so that the flow speed of the
exhaust gas flowing in the sub-exhaust passage RD does not exceed
the upper limit speed when the valve 44 is closed. More
specifically, the cross sectional area of the opening RC1 and the
total of the cross sectional areas of the openings RB2 are set in
the manner described in the following section (b).
(b) The total of the cross sectional areas of the openings RB2
(i.e., the total of the cross sectional areas of all the partition
holes 57H) is less than the cross sectional area of the opening
RC1. In addition, the total of the cross sectional areas of the
openings RB2 and the cross sectional area of the opening RC1 are
set so that exhaust gas flows at the required flow speed.
(c) The opening RC1 and the openings RB2 are positioned so that the
difference in pressure between the space upstream of the opening
RC1 and the space downstream of the openings RB2 does not become
excessively great. That is, the opening RC1 and the openings RB2
are positioned so that the pressure difference does not make the
speed of the exhaust gas flowing in the sub-exhaust passage RD
higher than the upper limit speed. More specifically, the opening
RC1 and the openings RB2 are positioned in the manner described in
the following section (d).
(d) The openings RB2 are positioned so as to allow exhaust gas to
flow between the sub-exhaust passage RD and the space where exhaust
gas swirls or stagnates inside the absorption portion 5. Also, the
opening RC1 is positioned so as to allow exhaust gas to flow
between the space 45A inside the valve portion 4 and the
sub-exhaust passage RD.
The modes where the exhaust gas flows in the catalytic-converter 3
will be described with reference to FIG. 19 and FIG. 20.
An electronic control unit determines whether the three-way
catalyst of the catalytic-converter 21 is active in the exhaust
system for the engine 1 in this embodiment. If it is determined
that the three-way catalyst is not active, the electronic control
unit selects a cold-catalyst mode to keep the valve 44 closed. If
it is determined that the three-way catalyst is active, the
electronic control unit selects a warm-catalyst mode to keep the
valve 44 open. The electronic control unit determines whether the
three-way catalyst is active based on the operating state of the
engine 1.
[1] FIG. 19 illustrates the flow of the exhaust gas when the
cold-catalyst mode (first mode) is selected. When the cold-catalyst
mode is selected, exhaust gas flows in the catalytic-converter 3 as
follows.
[a] The exhaust gas in the second exhaust pipe 24 flows into the
space 45A inside the valve portion 4 through the opening of the
second exhaust pipe 24 (i.e., the inlet port RE).
[b] The exhaust gas in the space 45A inside the valve portion 4
flows into the sub-exhaust passage RD through the opening RC1.
[c] The exhaust gas in the sub-exhaust passage RD passes through
the hydrocarbon-absorbent 55, and then flows into the space 56
inside the absorption portion 5 through the openings RB2. The
hydrocarbon-absorbent 55 absorbs hydrocarbon present in the exhaust
gas when the exhaust gas passes through the hydrocarbon-absorbent
55.
[d] The exhaust gas in the space 56 inside the absorption portion 5
passes through the three-way catalyst 64, and then flows into the
third exhaust pipe 25. The three-way catalyst 64 removes nitrogen
oxide and carbon monoxide present in the exhaust gas when the
exhaust gas passes through the three-way catalyst 64.
Thus, all of the exhaust gas flowing into the catalytic-converter 3
passes through the hydrocarbon-absorbent 55 and then passes through
the three-way catalyst 64 when the cold-catalyst mode is selected.
This reduces the amount of hydrocarbons released to the
atmosphere.
[2] FIG. 20 illustrates the flow of the exhaust gas when the
warm-catalyst mode (second mode) is selected. When the
warm-catalyst mode is selected, the mainstream and sidestream of
exhaust gas both flow. Solid lines in FIG. 20 indicate the
mainstream. Dashed lines in FIG. 20 indicate the sidestream.
The mainstream of exhaust gas flows as follows.
[a] The exhaust gas in the second exhaust pipe 24 flows into the
space 45A inside the valve portion 4 through the opening of the
second exhaust pipe 24 (i.e., inlet port RE).
[b] The exhaust gas in the space 45A inside the valve portion 4
flows into the main exhaust passage RA through the valve 44 and the
opening RA1.
[c] The exhaust gas in the main exhaust passage RA flows into the
space 56 inside the absorption portion 5 through the opening
RA2.
[d] The exhaust gas in the space 56 inside the absorption portion 5
passes through the three-way catalyst 64, and then flows into the
third exhaust pipe 25. The three-way catalyst 64 removes nitrogen
oxide, carbon monoxide, and hydrocarbons present in the exhaust gas
when the exhaust gas passes through the three-way catalyst 64.
The sidestream of exhaust gas flows as follows.
[a] The exhaust gas in the space 56 inside the absorption portion 5
flows into the sub-exhaust passage RD through the openings RB2.
[b] The exhaust gas flows in the sub-exhaust passage RD from the
downstream side to the upstream side, and passes through the
hydrocarbon-absorbent 55. When the exhaust gas passes through the
hydrocarbon-absorbent 55, hydrocarbons that have been captured by
the hydrocarbon-absorbent 55 are released from the
hydrocarbon-absorbent 55, and the hydrocarbons released flow toward
the upstream together with the exhaust gas.
[c] The exhaust gas in the upstream of the sub-exhaust passage RD
flows into the 45A inside the valve portion 4 through the opening
RC1.
[d] The exhaust gas in the space 45A inside the valve portion 4
flows into the mainstream at the space upstream of the valve
44.
Thus, when the warm-catalyst mode is selected, hydrocarbon released
from the hydrocarbon-absorbent 55 is carried by the sidestream, and
then the hydrocarbons are mixed with the mainstream at the space
upstream of the valve 44. When the mainstream passes through the
three-way catalyst 64, the three-way catalyst 64 removes the
hydrocarbons released.
The exhaust gas control apparatus for an engine according to the
invention (i.e., the catalytic-converter 3) has the effects
described below.
(1) In the catalytic-converter 3 in this embodiment, the valve
portion 4, the absorption portion 5, and the catalyst portion 6 are
independent of each other. Also, the valve portion 4, the
absorption portion 5, and the catalyst portion 6 are disposed in
series. With this configuration, each of the valve portion 4, the
absorption portion 5, and the catalyst portion 6 can be replaced
with another corresponding portion that achieves the required level
of performance, independently of the other portions. For example,
the size of the three-way catalyst 64 can be changed without
replacing the hydrocarbon-absorbent 55. Thus, with this
configuration, any component can be replaced with another
corresponding component that achieves the required level of
performance while minimizing the number of other components to be
replaced.
(2) In the catalytic-converter 3 in this embodiment, when the valve
44 is open, hydrocarbon released from the hydrocarbon-absorbent 55
is sufficiently mixed with the exhaust gas in the mainstream before
reaching the three-way catalyst 64. This improves the efficiency of
the three-way catalyst 64 in removing hydrocarbons.
(3) In the catalytic-converter 3 in this embodiment, when the valve
44 is open, exhaust gas stably flows in the sub-exhaust passage RD
from the downstream side to the upstream side.
(4) In the catalytic-converter 3 in this embodiment, the
hydrocarbon concentration in the exhaust gas passing through the
three-way catalyst 64 does not greatly vary. This improves the
efficiency in removing hydrocarbons.
(5) In the catalytic-converter 3 in this embodiment, the
hydrocarbon content of the exhaust gas in the mainstream is equal
to or less than the upper limit value at or below which the
three-way catalyst 64 can absorb all of hydrocarbon present in the
exhaust gas. With this configuration, the three-way catalyst 64 can
appropriately remove hydrocarbons.
(6) In the catalytic-converter 3 in this embodiment, the flow speed
of the exhaust gas passing through the sub-exhaust passage RD is
maintained at a value less than the upper limit speed when the
valve 44 is closed. With this configuration, the
hydrocarbon-absorbent 55 can sufficiently absorb hydrocarbons.
(7) In the catalytic-converter 3 in this embodiment, the three-way
catalyst 64 is provided downstream of the opening RB2 to increase
the pressure in the space downstream of the openings RB2. Because
the three-way catalyst 64 is used as the resistance, the size of
the catalytic-converter 3 does not need to be increased.
(8) In the catalytic-converter 3 in this embodiment, the opening of
the second exhaust pipe 24, which functions as the inlet port RE,
is opened to the space 45A inside the valve portion 4. That is, the
inlet port RE is disposed immediately upstream of the valve 44. By
using the opening of the second exhaust pipe 24 as the inlet port
RE, another member is not required. This improves productivity.
A production method for the catalytic-converter 3 will be
described. The catalytic-converter 3 is produced in steps 1 through
5. [First step] The valve portion 4 that achieves the required
level of performance is selected from among different valve
portions that achieve different levels of performance. [Second
step] The absorption portion 5 that achieves the required level of
performance is selected from among different absorption portions
that achieve different levels of performance. [Third step] The
catalyst portion 6 that achieves the required level of performance
is selected from among different catalyst portions that achieve
different levels of performance. [Fourth step] The selected valve
portion 4, absorption portion 5, and catalyst portion 6 are
disposed in series and are joined to each other. [Fifth step] The
second exhaust pipe 24 is disposed such that the opening of the
second exhaust pipe 24 at the downstream side thereof (i.e., the
inlet port RE) is opened to the space 45A inside the valve portion
4. Then, the second exhaust pipe 24 is joined to the valve portion
4.
Producing the exhaust gas control apparatus for an engine in this
embodiment according to the described method results in the
following effects.
(9) According to the method in this embodiment, different types of
catalytic-converters 3 with the absorbent that achieve different
levels of performance may be produced by replacing any individual
component with another corresponding component that achieves the
required level of performance while minimizing the number of other
components to be replaced.
The aforementioned embodiment can be appropriately changed as
follows.
In a first modified example of the aforementioned embodiment, as
shown in FIG. 21, the second exhaust pipe 24 includes a plurality
of holes 71 which allow exhaust gas to radially flow between the
inside and the outside of the second exhaust pipe 24. By forming
the holes 71 in the second exhaust pipe 24, the flow speed of the
exhaust gas flowing in the sub-exhaust passage RD (i.e., the amount
of hydrocarbons released from the hydrocarbon-absorbent 55) can be
adjusted. When employing this configuration, the method for
producing the catalytic-converter 3 includes a step of forming the
holes 71 in the second exhaust pipe 24. This step is performed
before the fifth step is performed. With this configuration, the
flow speed of the exhaust gas can be adjusted to the required speed
without replacing the valve portion 4 or the absorption portion 5.
This improves productivity.
In the aforementioned embodiment, by providing the second exhaust
pipe 24 in the space 45A inside the valve portion 4, the opening of
the second exhaust pipe 24, which functions as the inlet port RE,
is disposed immediately upstream of the valve 44. However, for
example, the embodiment can be changed as follows. An
auxiliary-exhaust pipe that is independent of the second exhaust
pipe 24 is connected to an end of the second exhaust pipe 24 at the
downstream side thereof, and this auxiliary pipe is disposed in the
space 45 inside the valve portion 4. The opening of the
auxiliary-exhaust pipe, which is disposed immediately upstream of
the valve 44, functions as the inlet port RE.
When employing the aforementioned configuration, by forming holes
that allow exhaust gas to radially flow between the inside and the
outside of the auxiliary-exhaust pipe, the flow speed of the
exhaust gas flowing in the sub-exhaust passage RD can be adjusted.
When employing this configuration, the method for producing the
catalytic-converter 3 includes a step of forming the holes in the
auxiliary-exhaust pipe. This step is performed before the
auxiliary-exhaust pipe is disposed in the space 45A inside the
valve portion 4.
In the aforementioned embodiment, the three-way catalyst 64 is used
as the resistance. In a second modified example of the embodiment,
as shown in FIG. 22, a sound-absorbing material (glass wool) 72 is
disposed downstream of the openings RB2. With this configuration,
the sidestream reliably flows in the sub-exhaust passage RD, and
the catalytic-converter 3 also functions as a muffler.
In a third modified example of the embodiment, as shown in FIG. 23,
the internal cylinder 54 of the absorption portion 5 has a tapered
shape such that the cross sectional area thereof (i.e., the cross
sectional area orthogonal to the axis thereof) increases from the
upstream side to the downstream side. With this configuration,
exhaust gas is less likely to swirl or stagnate. This reduces the
backpressure of the engine 1. Also, exhaust gas uniformly flows
into the entire area of the three-way catalyst 64. This improves
efficiency in purifying exhaust gas.
Further, in a fourth modified example of the embodiment, as shown
in FIG. 24, the internal cylinder 54 of the absorption portion 5
includes an external pipe 54a and an internal pipe 54b. The
external pipe 54a contacts the catalyst portion 6. The internal
pipe 54b is concentrically disposed within the external pipe 54a. A
space 58 is formed between the external pipe 54a and the internal
pipe 54b. That is, one end of the internal pipe 54b is fixed to the
inner surface of the external pipe 54a at the upstream side
thereof. A wire mesh 59 is provided between the other end of the
internal pipe 54b and the inner surface of the external pipe 54a at
the downstream side thereof. The wire mesh 59 offsets the
difference in thermal expansion between the external pipe 54a and
the internal pipe 54b. With this configuration, the space 58 serves
as a heat-insulating layer. Therefore, when the valve 44 is open,
the heat from exhaust gas flowing in the main exhaust passage RA is
unlikely to be transmitted to the hydrocarbon-absorbent 55 disposed
outside the external pipe 54a. This reduces the possibility that
the increase in temperature of the hydrocarbon-absorbent 55 will
cause all the hydrocarbons captured to be released from the
hydrocarbon-absorbent 55 all at once. That is, hydrocarbons
captured is gradually released from the hydrocarbon-absorbent 55 by
suppressing the increase in the temperature of the
hydrocarbon-absorbent 55. This improves efficiency of the catalyst
in removing hydrocarbons. The heat-insulating effect may be
improved by providing a heat-insulating material in the space
58.
In this case, preferably, the diameter of the portion of the
internal pipe 54b is gradually reduced going from the upstream side
toward the downstream side thereof, as shown in FIG. 24. With this
configuration, the high-temperature exhaust gas passing through the
internal cylinder 54 of the absorption portion 5 does not directly
contact the inner surface of the internal pipe 54b. This reduces
the amount of heat transmitted to the internal pipe 54b from the
exhaust gas flowing in the main exhaust passage RA. Thus, by
employing this configuration, the heat-insulating effect can be
further improved.
While the invention has been described with reference to example
embodiments thereof, it is to be understood that the invention is
not limited to the example embodiments or constructions. To the
contrary, the invention is intended to cover various modifications
and equivalent arrangements. In addition, while the various
elements of the example embodiments are shown in various
combinations and configurations, other combinations and
configurations, including more, less or only a single element, are
also within the spirit and scope of the invention.
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